We plan to investigate functional relations between motor cortex cells and individual arm muscles by recording their activity in awake rhesus monkeys operantly conditioned to perform the following response patterns: (a) with the arm semi-prone in a hinged cast the monkey will actively flex and extend both the wrist and the elbow against a programmed load; (b) with the arm relaxed, comparable passive movements will be imposed by a servo-motor; (c) with the arm held isometrically the monkey will be trained to make isolated contractions of each of 4 major muscles, and (d) to generate bursts of cortical cell activity. Response averages of unit and muscle activity, position and force will be compiled for each response condition to determine the strongest and most consistent unit-muscle correlations. These will be tested by conditioning dissociation of the correlated elements. Cell and muscle activity will also be cross-correlated to investigate the extent of functional connections between single PT cells and different arm muscles. In monkeys with chronic precentral epileptic foci we will investigate mechanisms underlying synchronous burst activity of epileptic cells. The extent of correlated activity will be documented by recording simultaneously from multiple points in the focus; firing patterns of epileptic cells will be investigated during active movements and during operantly conditioned changes in interictal cell activity. The possible effects of these procedures on seizure frequency will also be documented. We also plan to study the effects of the corticospinal tract on identified cells in cervical spinal cord of awake monkeys. We will characterize the cells' responses to natural stimulation, and electrical stimulation of brachial plexus nerves and pyramidal tract, and document their responses during active and passive wrist movements.